Current steering element, storage element, storage device, and method for manufacturing current steering element

Abstract

A current steering element which can prevent occurrence of write disturb even when electric pulses having different polarities are applied and can cause large current to flow through a variable resistance element, and with which data can be written without problem. In a storage element (3) including: a variable resistance element (1) whose electric resistance value changes in response to application of electric pulses having a positive polarity and a negative polarity and which maintains the changed electric resistance value; and the current steering element (2) that steers current flowing through the variable resistance element (1) when the electric pulses are applied, the current steering element (2) includes: a first electrode (32); a second electrode (31); and a current steering layer (33) interposed between the first electrode (32) and the second electrode (31). When the current steering layer (33) includes SiNx (0<x≰0.85) and a thickness of d [nm], a relationship between a nitrogen composition ratio x and the thickness d is in a range represented by a predetermined conditional expression.

1. A current steering element which steers passing current that flows when electric pulses having a positive polarity and a negative polarity are applied, said current steering element comprising:
 a first electrode; 
 a second electrode; and 
 a current steering layer interposed between said first electrode and said second electrode, 
 wherein, when said current steering layer includes SiN x  in which x denotes a nitrogen composition ratio and is within a range of 0<x≦0.85 and has a thickness of d nanometer, and a maximum value of a voltage that can be applied between both ends of said current steering element is V o  volt, a relationship between the nitrogen composition ratio x and the thickness d is in a range that satisfies Expression (1) and Expression (2), the Expression (1) being (ln(10000(C exp(αd)exp((βx)) −1 )/γ) 2 ≦V 0 , and the Expression (2) being (ln(1000(C exp(αd)exp((βx)) −1 )/γ) 2 −(ln(10000(C exp(αd)exp((βx)) −1 )/γ) 2 /2≧0, where C=7.46×10 −2 , α=−6.25×10 −1 , β=−11.7, γ=9.76. 
 
     
     
       2. The current steering element according to  claim 1 , wherein the thickness d of said current steering layer is equal to or larger than 5 nm. 
     
     
       3. The current steering element according to  claim 1 , wherein said first electrode and said second electrode include tantalum nitride or alpha-tungsten. 
     
     
       4. A storage element comprising:
 a variable resistance element which is non-volatile and has an electric resistance value reversibly changes in response to application of electric pulses having a positive polarity and a negative polarity; and 
 said current steering element according to  claim 1 , said current steering element being connected in series to said variable resistance element and steering passing current that flows when the electric pulses are applied to said variable resistance element. 
 
     
     
       5. A storage device comprising:
 a plurality of bit lines; 
 a plurality of word lines each of which three-dimensionally crosses a corresponding one of said plurality of bit lines; and 
 a plurality of storage elements including said storage element according to  claim 4 , 
 wherein each of said plurality of storage elements is provided at a corresponding one of crosspoints at which said plurality of bit lines and said plurality of word lines three-dimensionally cross each other, and has one end connected to a corresponding one of said plurality of bit lines and an other end connected to a corresponding one of said plurality of word lines. 
 
     
     
       6. A method of manufacturing a current steering element which includes: a first electrode; a second electrode; and a current steering layer including SiN x  interposed between the first electrode and the second electrode, and which steers current that flows when electric pulses having a positive polarity and a negative polarity are applied, said method comprising:
 designing the current steering element by determining a thickness d and a nitrogen composition ratio x of the current steering layer; and 
 manufacturing the current steering element according to the thickness d and the nitrogen composition ratio x determined in said designing, 
 wherein said designing includes: 
 obtaining: a lowest current density J min  (A/cm 2 ) of current necessary to flow through the current steering element; a maximum allowable current density J off  (A/cm 2 ) of current that flows through the current steering element when the current steering element is in a shut off state; and a maximum value V 0  (volt) of a voltage that can be applied between both ends of the current steering element; and 
 determining the thickness d and the nitrogen composition ratio x which are in a range that satisfies Expression (3) and Expression (4), using the current density J min , the current density J off , and the V 0  which have been obtained in said obtaining, the Expression (3) being (ln(J min (C exp(αd)exp(βx)) −1 )/γ) 2 ≦V 0 , and the Expression (4) being (ln J off (C exp(αd)exp(βx)) −1 )/γ) 2 −(ln(J min (C exp(αd)exp(β)x) −1 )/γ) 2 /2≧0, where C=7.46×10 −2 , α=−6.25×10 −1 , β=−11.7, γ=9.76. 
 
     
     
       7. The method of manufacturing a current steering element according to  claim 6 ,
 wherein, in said determining, the thickness d and the nitrogen composition ratio x are determined such that the thickness d is equal to or larger than 5 nm and the nitrogen composition ratio x satisfies 0<x≦0.85. 
 
     
     
       8. The method of manufacturing a current steering element according to  claim 6 ,
 wherein said manufacturing includes: 
 forming the first electrode on a substrate, the first electrode including tantalum nitride or α-tungsten; 
 forming a SiN x  film on the first electrode, the SiN x  film having the thickness d and the nitrogen composition ratio x which have been determined in said designing; and 
 forming the second electrode on the SiN x  film, the second electrode including tantalum nitride or alpha-tungsten. 
 
     
     
       9. The current steering element according to  claim 1 ,
 wherein the SiNx forms an amorphous semiconductor.